Bug Fix #2 In Firefox Focus For iOS

November 12, 2018

One week ago, I wrote a story about my first bug fix in a privacy browser for iOS from Mozilla called Firefox Focus. In that article, you can also find out my introduction of Firefox Focus.

If you missed my previous story, I highly recommend you to read it.

Firefox Focus iOS version 8.0 is going to be released soon. This new release will mainly have enhancements for search suggestions feature of the browser. I worked on one of the bugs in search suggestions.


URL Bar does not display the search text if a user selects search suggestion instead of pressing the “Go” button on the keyboard. Here is an example: If you search for mozilla and press the “Go” button, the URL Bar will contain mozilla. However, if you search for mozilla and you select one of search suggestions, the URL Bar will contain


My strategy to fix this bug was:
1. Find a function that is called on a search suggestion click.
2. Debug this function and understand how it works.
3. Find the code that sets the text to URL bar.
4. Make changes to fix the bug.

Firefox Focus has a helpful document called UI and Code Map in their documentation. This document basically maps UI to the code, and it is very useful for new contributors who are not very familiar with the codebase of the project.

In that document, I found that the view that contains suggestions is called OverlayView.

It let me start my investigation. I went through the OverlayView class in the app. In OverlayView.swift, I found the OverlayViewDelegate protocol declaration. This protocol contains a bunch of functions that are supposed to respond to different user actions.

Two of the functions above were under my suspicion: didSearchForQuery and didSubmitText. I found their implementation in the BrowserViewController.

I created two breakpoints on each of them, and went through the scenario to reproduce the bug. As I found, didSearchForQuery is called when the user selects a suggestion. Now, I had to debug this function and find the piece of code that sets the text of URL Bar. If you take a look at the implementation of didSearchForQuery, you will see that it is not so big.

However, when you debug this function, it goes deeper and deeper, and it goes into so many other functions. I also compared didSearchForQuery to its analogue function that is called when the user presses “Go” button. I found that they are similar between each other, and eventually they call a function called setTextToUrl, and I thought it is exactly what I am looking for.

I spent some time playing with the code and making different changes. I thought I found the reason why didSearchForQuery didn’t change the text in URL Bar because I noticed that it didn’t push the search to SearchHistory stack, so consequently, the setTextToUrl function couldn’t get value. I added a method to didSearchForQuery that pushed search to SearchHistory stack, and it seemed like setTextToUrl function was getting the value of the current search, however, URL Bar still contained! I was confused and tried to find the solution, but my tries weren’t successful, so I decided to ask project maintainers.

I wrote about my investigation of the problem, and the steps I made to resolve it in the issue on GitHub. I heard back very soon from the maintainer Sawyer Blatz.

He gave me an advice how to fix this issue. It turned out that the fix is easier than I thought, I just had to change the line in didSearchForQuery:

submit(url: url)


urlBar(urlBar, didSubmitText: query)

This change basically calls the function that is used when the user presses the keyboard’s “Go” button. It worked!

As you can see, if the user selects a search suggestion, the search text is displayed in URL Bar.


My pull request was successfully merged ✅

It was fun experience fixing this bug. I am becoming more and more familiar with Focus codebase, and it makes me feel confident because I plan to work on other issues there in the future.

Also, I would like to point out that is was so nice of Sawyer to explain why my code didn’t work. It’s my third contribution to Mozilla’s projects (I also contributed to Mozilla add-ons), and I noticed that Mozilla’s community is very kind to every contributor. I believe that it is one of the major factors that attracts developers to make contributions to their projects.